Refrigeration system defrost control



Sept. 10, 1968 G. B. ORBESEN REFRIGERATION SYSTEM DEFROST CONTROL Filed April 20, 1967 FIG. I

FIG. 2

m w mm E0 W B BYWZ7ZM ATTORNEY.

3,400,553 REFRIGERATION SYSTEM DEFROST CONTROL Gordon B. Orbesen, Bridgeport, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Apr. 20, 1967, Ser. No. 632,380 4 Claims. (Cl. 62-155) ABSTRACT OF THE DISCLOSURE A control for time-temperature based heat pump defrosting systems effective to hold the control timing mechanism in an actuated position following lapse of a preset timed interval thereby placing the defrosting system in condition for immediate actuation pending icing of the heat pump outdoor coil.

Background of the invention This invention relates to a control arrangement for refrigeration systems, and more particularly to a control arrangement for refrigeration systems of the type selectively operable to either cool or heat.

Reverse cycle refrigeration systems, commonly called heat pumps, normally include some mechanism for defrosting the outdoor coil to restore system heating efficiently lost through the build-up of frost and/or ice on the outdoor coil.

Since defrosting the outdoor coil is usually at the expense of the system heating capacity as, for example, where defrosting is effected by reverting the system to cooling cycle operation, the duration of the defrost cycle is usually closely controlled to obtain optimum defrost without excessive operation on the defrost cycle. Patents Nos. 3,170,304 and 3,170,305 illustrate a timing mechanism adapted to limit both the frequency and extent of the defrost cycle.

It is an object of the present invention to provide a new and improved defrost control arrangement for reverse cycle refrigeration systems.

It is a further object of the present invention to provide an improved control for time-temperature based heat pump defrosting systems which reduces the potential lag between icing of the outdoor coil and actuation of the defrosting system.

It is an additional object of the present invention to provide an improved control arrangement for heat pumps employing a time-temperature based defrost control effective to permit more rapid initiation of the defrost cycle following the accumulation of frost and/or ice on the outdoor coil.

Summary of the invention This invention relates to a reverse cycle refrigeration system of the type having compression means, an outdoor coil, refrigerant metering means, and an indoor coil adapted upon operation of the compression means to cool; with means to reverse the flow of refrigerant through the indoor coil, the refrigerant metering means, and the outdoor coil whereby the system heats; comprising in combination, means for defrosting the outdoor coil; means for regulating the defrosting means including outdoor coil condition sensing means operating at a preset outdoor coil icing condition; a timing mechanism; a timer control adapted to be periodically operated by the timer mechanism, concurrent operation of the outdoor condition coil sensing means and the timer control actuating the defrosting means to commence defrosting of the outdoor coil; and a defrost limit control operated by the timer mechanism after the timer control to terminate outdoor coil defrosting regardless of outdoor coil icing conditions, the timer mechanism being arranged to main- United States Patent "ice 3,400,553 Patented Sept. 10, 1968 tain the timer control actuated for a relatively short interval to enable the defrost limit control to limit the duration of outdoor coil defrosting; and control means responding to actuation of the timer control to stop the timing mechanism whereby the timer control may be maintained in actuated position enabling immediate actuation of the defrosting means upon subsequent operation of the outdoor coil condition sensing means.

Brief description of the drawings FIGURE 1 is a diagrammatic view of a reverse cycle refrigeration system forming the subject of this invention; and

FIGURE 2 is a wiring diagram of an electric circuit for controlling the reverse cycle refrigeration system shown in FIGURE 1.

Description 0 the preferred embodiment Referring particularly to FIGURE 1 of the drawings, there is illustrated an air-to-air heat pump employed in a refrigeration system operable on the reverse cycle principle. In an apparatus of this type, a first heat transfer coil is disposed within or in communication with the area to be conditioned, and a second heat transfer coil is located within tor in communication with the outdoors.

Refrigerant compressor 10 discharges relatively hot gaseous refrigerant through discharge line 11 to reversing means 12. Reversing means 12 is preferably a four-way reversing valve adapted to reverse the refrigerant flow through a portion of the system in order to obtain the desired heating effect as will be more apparent hereinafter. In the position shown in FIGURE 1 of the drawings, reversing means 12 routes, during cooling cycle operation, the hot gaseous refrigerant through line 14 to outdoor heat transfer coil 15 wherein the gaseous refrigerant is condensed by the outdoor air passed over coil 15 by fan 20.

Condensed liquid refrigerant from coil 15 passes through suitable expansion means 16 to indoor heat transfer coil 17, serving as an evaporator during cooling cycle operation. Line 22 may have a suitable check valve control 27 adapted to admit flow in a direction shown by the solid line arrow of the drawing to bypass refrigerant around second expansion means 28. The expansion means 16 provides the liquid pressure drop between the system transfer coils during cooling cycle operation.

In indoor heat transfer coil 17, refrigerant is vaporized as heat is extracted from the stream of air delivered over coil 17 by fan 21. Vaporous refrigerant from coil 17 returns through line 18, reversing means 12, and suction line 19 to compressor 10 to complete the refrigerant cycle. Fans 20, 21 are driven by suitable driving means, such as electric motors.

To heat the area being conditioned, solenoid 13 is energized causing reversing means 12 to place indoor heat transfer coil 17 in communication with compressor discharge line 11 and outdoor heat transfer coil 15 in communication with compressor suction line 19. Under these circumstances, heat from the hot gaseous refrigerant passing through indoor heat transfer coil 17 is rejected to the air flowing thereover. The rejection of heat by the refrigerant converts the gaseous refrigerant to liquid. Liquid refrigerant from coil 17 passes through expansion means 28 to outdoor heat transfer coil 15, now functioning as an evaporator. Line 29 may have a check valve control 31 therein adapted to permit flow of refrigerant in a direction shown by the solid line arrow on control 31 in FIG- URE l to bypass refrigerant around expansion means 16. The vaporous refrigerant generated in coil 15 as a result of heat transfer between the refrigerant and outdoor air returns through reversing means 12 and suction line 19 to compressor 10. It is understood that expansion means 28 provides the liquid pressure drop between the indoor and outdoor heat transfer coils during heat cycle operation.

Referring to FIGURE 2 of the drawings, leads L L are connected to a suitable source of electrical energy (not shown). As will be apparent to those skilled in the art, the circuit shown in FIGURE 2 may be readily modified for operation from a three-phase power source.

Compressor 10, indoor fan and outdoor fan 21 are connected in parallel with one another through cooling thermostat 32 across leads L L Heating thermostat 34 parallels cooling thermostat 32. Heating and cooling thermostats 32, 34 respond to temperature conditions of the area being conditioned, cooling thermostat 32 being arranged to respond to a predetermined high temperature condition within the area conditioned, while heating thermostat 34 is arranged to respond to a predetermined low temperature condition within the area conditioned. Additionally, the energizing circuit for reversing means solenoid 13 is series connected with heating thermostat 34 across leads L L A manual control switch 30, when moved to the dotted line position in FIGURE 2, connects indoor fan 20 directly across leads L L to provide continuous indoor fan operation irrespective of the area conditions sensed by thermostats 32, 34.

Defrost control switch 35 is in series with the energizing circuits of outdoor fan 21 and solenoid 13. As will be more apparent hereinafter, during the defrost cycle, switch 35 opens to interrupt the energizing circuits to fan 21 and solenoid 13.

With manual control switch in the solid line position of FIGURE 2 of the drawings, and defrost control switch closed, on a demand for cooling, thermostat 32 completes energizing circuits to compressor 10, indoor fan 20 and outdoor fan 21. The system accordingly operates to cool the area being conditioned.

On a demand for heating, thermostat 34 responds to complete the energizing circuits to compressor 10, indoor fan 20, and, assuming defrost control switch 35 to be closed, to outdoor fan 21 and reversing means solenoid 13. The system accordingly heats.

Defrost control switches 35, 37, 49 are controlled by defrost control relay 40, series connected through outdoor coil temperature responsive switch 42, timer switch 44, and switch 37 across leads L L A suitable timing device, i.e. motor 48, is connected by defrost control switch 49 across leads L L When energized, defrost control relay 40 opens switch 35 to interrupt the energizing circuits to fan 21 and solenoid 13 while closing switches 37, 49. Closure of switch 49 completes an energizing circuit to timing device 48.

A timer switch is arranged in parallel with defrost control switch 49. Timer switch 52 parallels defrost control switch 37. The timing device 48, when continuously operated, will periodically open timer switch 50 and close timer switch 52 for a brief interval. After the lapse of a predetermined time interval following actuation of switches 50, 52, timing device 48 opens timer switch 44 for a short interval. As an exemplary time schedule, timer switches 50, 52 may be opened and closed respectively at ninety minute intervals while timer switch 44 is opened approximately ten minutes after actuation of switches 50, 52.

As will be more apparent hereinafter, if temperature responsive switch 42 is open when timing device 48 actuates switches 50, 52, timing device 48 is rendered inoperative by the opening of switch 50. In that event, switches 50, 52 are held in their open and closed positions respectively until the timing mechanism 48 is restarted. And the time interval within which switch 44 is actuated is extended by the shutdown time of timing device 48.

Control operation Assuming timer switch 50 is closed, a circuit from lead L through switch 50 to lead L is completed, energizing the timing device 48. Following the lapse of a predetermined time interval, i.e. ninety minutes, timing device 48 closes switch 52 and opens switch 50. Assuming switch 49 to be open, the energizing circuit to timing device 48 is broken and timing device 48 stops with timer switch 52 in closed position.

During operation of the system on the heating cycle, ice may accumulate on outdoor coil 15 with a consequent decrease in system heating effectiveness. The accumulation of ice on the outdoor coil may be sensed by monitoring outdoor coil temperatures, it being understood that as ice builds up, coil temperatures decrease. Thermostatic switch 42, which is arranged to sense outdoor coil temperatures, closes at a preset low outdoor coil temperature to complete a circuit from lead L through timer switches 52, 44 and switch 42 to lead L energizing defrost control relay 40. It is understood that where, on closure of thermostatic switch 42, timer switch 52 is open, energization of defrost control relay 40 is delayed until timer switch 52 closes. When energized, defrost control relay 40 opens switch 35, interrupting the circuit to outdoor fan 21, and, at the same time, interrupting the circuit to reversing means solenoid 13 permitting reversing means 12 to assume cooling cycle position. Compressor 10 remains energized through heating thermostat 34, and the system effectively reverts to cooling cycle operation. Accordingly, relatively hot gaseous refrigerant discharged by compressor 10 is routed by reversing means 12 to outdoor coil 15 warming coil 15 and melting ice formed thereon.

As ice on outdoor coil 15 melts, temperatures of coil 15 rise, and at a predetermined high outdoor coil temperature, thermostatic switch 42 opens. Opening of switch 42 interrupts the energizing circuit to defrost control relay 40, closing switches 35, 37 whereby the system reverts to normal heating cycle operation.

Closure of defrost control switch 49 by defrost control relay 40 at the start of the defrosting cycle completes an energizing circuit to timing device 48. When restarted, timing device 48 quickly closes timer switch 50 and opens timer switch 52. Defrost switch 37 retains defrost control relay 40 energized upon opening timer switch 52.

Following the lapse of a preset time interval, i.e. ten minutes, timing device 48 opens timer switch 44. If thermostatic switch 42 is then closed, opening of timer switch 44 interrupts the energizing circuit to defrost control relay 40 to terminate the defrost cycle. Should thermostatic switch 42 open before switch 44, the subsequent opening of timer switch 44 is without effect.

The deenergization of defrost control relay 40 by opening of timer switch 44 or switch 42, permits the system to revert to heating cycle operation (assuming heating thermostat 34 is closed).

As described heretofore, and assuming switch 42 to be opened, timing device 48, following the lapse of a preset time interval, i.e. ninety minutes, closes timer switch 52. At the same time, timer switch 50 is opened to stop timing device 48 so as to maintain timer switch 52 in a closed position. Closure of thermostatic switch 42 subsequent to closure of switch 52 and opening of switch 50 initiates the defrost cycle without delay as explained heretofore. Should thermostatic switch 42 close during the time interval before closure of switch 52, startup of the defrost cycle awaits closure of switch 52.

As can be understood from the preceding description, the function of timer switch 44 in limiting the maximum length of the defrost cycle requires that timer switch 52 be only momentarily closed when initiating the defrost cycle. If timer switch 52 is held closed by the timing mechanism 48 for a longer period, the defrost cycle could be prematurely restarted on reclosure of timer switch 44 if outdoor coil temperature responsive switch 42 were then closed. Excessive .defrost cycle operation reduces over-all system efficiency. On the other hand, limiting closure of timer switch 52 to a relatively short interval during each time interval may result in an inordinately long delay in the initiation of the defrost cycle. By the present invention the advantages accruing from the momentary actuation of timer switch 52 without the disadvantages of extended delay are realized.

While I have described preferred embodiments of the present invention, it is understood that this invention may be otherwise embodied within the scope of the following claims.

I claim:

1. In a reverse cycle refrigeration system of the type having compression means, an outloor coil, refrigerant metering means, and an indoor coil adapted upon operation of the compression means to cool, with means to reverse the flow of refrigerant through said indoor coil, said refrigerant metering means, and said outdoor coil whereby said system heats, the combination of: means for defrosting said outdoor coil; means for regulating said defrosting means including outdoor coil condition sensing means operating at a preset outdoor coil icing condition, a timing mechanism, a timer control adapted to be periodically operated by said timing mechanism, concurrent operation of said outdoor coil condition sensing means and said timer control actuating said defrosting means to commence defrosting of said outdoor coil, and a defrost limit control operated by said timer mechanism after said timer control to terminate outdoor coil defrosting regardless of outdoor coil icing conditions, said timer mechanism being arranged to maintain said timer control actuated for a relatively short interval to enable said defrost limit control to limit the maximum length of outdoor coil defrosting; and control means responding to actuation of said timer control to stop said timing mechanism whereby said timer control may be maintained in actuated position enambling immediate actuation of said defrosting means upon subsequent operation of said outdoor coil condition sensing means.

2. A system according to claim 1 including second control means adapted upon actuation of said outdoor coil defrosting means to restart said timing mechanism.

3. A system according to claim 2 in which said first control means includes a circuit for energizing said timing mechanism and a control switch for said circuit operable to interrupt said circuit and to deenergize said timer mechanism upon actuation of said first timer means.

4. A system according to claim 3 in which said second control means includes a second circuit for energizing said timing mechanism and a second control switch for said second circuit operable to complete said second circuit and energize said timing mechanism upon commencement of said outdoor coil defrosting.

MEYER PERLIN, Primary Examiner. 

